March 16, 1958 was an auspicious day if you were a telephone subscriber in the Seattle-metro area. On that date, telephone numbers
changed from 2 letters + 4 digits to 2 letters + 5 digits. The all-numeric numbers that we're used to now, over 50 years later had yet to
appear. Telephone numbers had a named prefix, and you dialed the first two letters of that prefix name plus the following digits. The prefix
names (a mnemonic device) were designed to help us remember the number, and the names came from a list of preferred names that Ma Bell kept. In some cases, especially
where there was some local item or locale of prominence, exceptions would be made. For example, the RAinier prefix was allowed due to the Rainier Valley and
Mount Rainier.

When the change happened, telephone numbers changed, like this:

FRanklin 1212 became EAst 4-1212.

The prefix changed from being just the name (FRanklin), to being the name and one associated digit (EAst 4).

During this transition, many prefixes disappeared completely as they were incorporated into the new prefix naming scheme. For instance, the old CApitol, EAst, FRanklin,
MInor exchanges all became part of the new EAst exchange. Exchange names were useful because they gave a clue to where that number was
physically located as well as being something people would recognize in speech. Personally, I also found them easier to remember. The central office
equipment (aka the telephone exchange) was located in buildings scattered throughout the city, so it made sense to distribute prefixes to specific geographic areas. That
concept still holds true today, although it is mostly for older wired telephones. The newer concept that you can take your phone number with you further dilutes this
concept and (of course) it is completely unapplicable for cell phones. In most cities in the US, the concept
of your telephone prefix identifying your neighborhood still holds true.

Today, there is so much demand for telephones that phone companies had to abandon named prefixes in favor of completely numeric telephone numbers. Why? Because it made
all combinations of numbers available for assignment as telephone numbers. Demand for numbers also forced multiple area codes into the plan.
Previously, area codes had 0 or 1 as the 2nd number, but this fell by the wayside.

If you like the concept of having a named prefix, you can still choose a name for your prefix (if the numbers allow it) from the old Bell Telephone list of
prefix names.